1. Technical Field
The present invention relates to a spectroscopic fundus measuring apparatus and a measuring method therefor. In particular, the present invention relates to a spectroscopic fundus measuring apparatus that acquires spectral fundus images to facilitate identification of parts with different spectral characteristics and that can form an image in which every part is clear in consideration of the spectral characteristics thereof, and a measuring method therefor.
2. Related Art
Fundus observation is doubtless important in ophthalmic diagnosis. At present, anomaly findings are obtained by diagnosing the eye fundus by means of colored fundus images, fluorescent contrast images, etc. from a fundus camera. If it is possible to measure quantitatively oxygen saturation degree on the fundus and constituent substances distributed in the retina, there is a possibility of finding out the functions of fine parts of the retina, which is considered to be greatly useful in clinical applications. Further, if spectral distribution of substances in the retina is clarified by spectral analyses, there is a possibility of analyzing the substances in the retina from the spectral images.
However, most of the studies carried out up to now are far from spectral image measurement in full-scale. Full-scale image measurement is considered to meet such conditions as: (a) being capable of obtaining high quality images, and (b) being capable of measuring spectral images with a higher degree of wavelength analysis over a wide wavelength band. Such an image measurement method is occasionally called hyper-spectral imaging. Advent of the liquid crystal wavelength tunable filter has made it possible to obtain spectral images relatively easily. Using a number of spectral images of different wavelengths makes it possible to examine spectral characteristics of substances in detail and to extract constituents having various known spectral distributions.
As a technique for identifying each part in a fundus image, a method for distinguishing retinal arteries and retinal veins based on red and green components in a fundus image has been disclosed. Also, a technique where the light beam reflected from a fundus is divided by wavelength into light beams within at least two wavelength regions in a wavelength range of 600 nm or more by a wavelength dividing means, fundus images of different wavelengths are photographed separately by a fundus photographing means, and a plurality of fundus images of different colors are superimposed to display one color image by a displaying means has been disclosed (see Patent Documents 1 and 2).    [Patent Document 1] JP-A-2001-145604 (paragraphs 0024 to 0091, FIG. 1 to FIG. 20)    [Patent Document 2] JP-A-Hei 8-71045 (paragraphs 0011 to 0032, FIG. 1 to FIG. 13)
While the hyper-spectral imaging is a technique in the spotlight and is used to obtain spectral images of the fundus, it is hard to perform accurate analyses because the amount of light of spectral images obtained varies greatly by the wavelength. Moreover, the hyper-spectral light separation with a light amount without putting burden on humans has yet to be realized.
A liquid crystal wavelength tunable filter, which was recently developed, is commercially available and can be used in spectroscopic imaging. When it is used, hyperspectral imaging of a retina can be easily achieved. However, as restricted by for example the wavelength tunable time of the liquid crystal wavelength tunable filter and the exposure time of the camera, it takes about 20 seconds to take images at every 10 nm in the wavelength range from 500 nm to 720 nm. Because alignment between the eye and the apparatus varies during that time, there has been another problem that the spectral images taken of the same part are displaced from each other.
The present inventors proposed an apparatus and method for measuring spectral fundus image data that can eliminate position displacement between spectral images of the same part even if change in alignment occurs between the eye and the apparatus with the lapse of time in Japanese Patent Application No. 2004-352093. However, there is still desired a spectroscopic fundus measuring apparatus capable of identifying parts with different spectral characteristics in a spectral fundus image easily and accurately and forming an image in which every part is clear and a method therefor.
An object of the present invention is to provide a spectroscopic fundus measuring apparatus capable of identifying each part in spectral fundus images easily and accurately based on its spectral characteristic and a measuring method therefor.